Production of coated sheet material



y 22, 1956 J. A. RUSH 2,746,878

PRODUCTION OF COATED SHEET MATERIAL Filed April 22, 1953 IN VEN TOR.

meg fi 1% United States 2,746,878 PRODUCTION OF COATED SHEET MATERIALApplication April 22, 1953, Serial No. 350,439 Claims. (Cl. 117'"15)This invention relates to the production of sheet material of novelcharacter.

. More particularly, the present invention relates to the coating of apaper of particular character, with an opacifying coating compositionadapted to provide a surface of enhanced printability, the whole afterbeing waxed being eminently suitable for and particularly adapted foruse as wrapping material for bread, cake, and the like. The printed andwaxed paper of the present invention is particularly characterized byits high gloss, sheen or brightness, striking legibility, enhancedesthetic effect, and softness.

Opaque, printed, waxed wrapping. papers of various character are knownand employed for the indicated purpose. Those heretofore known andemployed have, however, left much to be desired in brightness,legibility, and over-all eye or consumer appeal, primarily due to thenature of the paper base and the character of the coated or uncoatedsurface thereof towhich the printing. was of necessity applied andsubsequently waxed.

The production of the novel, opaque, printed, waxed wrapping papershaving the aforementioned superior properties is characterized byemployment of a specific paper base having a characterizing formationand surface structure, and the application thereto of a particularopacifying coating composition to result in a combination highlysusceptible to' fine, sharp, and clear-color printing due to itsextremely level and bright surface character. The nature of this surfaceis such that after waxing, the wax complements it to further brillianceand clearness; v I r The invention is further characterized bytheability' to opacify the'paper base and to provide an improvedprinting surface in one step by means of a single coating'c'omposition;the ability to carry out the operation at high speeds, such aspaper-making speeds so that the coating may be a continuous step in thepaper-making process if desired} the elimination of the necessityforsuper-calenderin'g; the manner and means for applying' the coating; andother advantages and economies as will hereinafter app'earfrom aconsideration of the following specification' and accompanyingdiagrammatic drawing.

enhance its The paper base employed in th'e'practice of the presentinvention ischara'ct'erizedby what is known as a machine glazed surfaceandi's'of a thin or tissue-like, translucent character, characteristicof-p'apers produced on a so-c'a'll ed' Yankee paper machine. Suchmachines have a dryer in the form of a steam-heated drum about 12 feetin diameterhaving a'highlyp'olished surface. A paper Web,afterfor'mation on a Fourdrinier wire, is'transferred in wet;approximately 70% moisture content condition, by

In of a-pair of felts a'nd' a couch" roll to the indicated drying drum;embraced about a major portion of" it's" printing and 2,746,878 PatentedMay 22, 1956 peripheral surface, and then stripped therefrom in a dry orsubstantially dry condition, i. e., from about 5% to about 15% finalmoisture content. If desired, the wet web from the Fourdrinier wire maybe predried to' a' moisture content of not less than about 50% beforebeing brought into contact with the indicated large diameter polisheddrying drum, when it is desired to produce paper at speeds greater thanabout 500 feet per minute.

The surface of the wet web which is brought into intimate contact withthe highly finished and heated'drum surface takes on a glazed or ironedappearance due to hot pressing of the wet web against the polished drumsurface. Although this web is of agenerally porous nature due to thecharacter of drying essentially against a single surface, the fibers atthe glazed web surface become smoothed or laid down to substantialparallelism with the web surface. The outer or opposed surface of theweb may be partially smoothed down during the drying operation by meansof rolls acting against the drum, and/ or by means of a calender afterbeing stripped from the drum.

In production of paper of this character and by the indicated means itis not desirable or economical to add all of the mineral fillers orpigments necessary for opacification to the paper stock, and thereforethe resultants'heet is translucent. If opaque paper is desired, suchtranslucent material must subsequently be coated. This can be done onthe Yankee dryer by applying an opacify ing coating composition to theouter face of the web as it passes over the dryer as shown, for example,in the Thiel and Richmond Patent 2,216,143 or Adrian Patent 2,313,497.The result is an opaque sheet having one coated surface and oneuncoat'ed machine glazed surface. 7 Such paper has been conventionallyemployed for bread and the like wrapping paper by printing on the glazedglazed surface, per se, is not, however, very receptive to fine, sharpprinting and the overcoat of wax results inand upon final waxing it ispossessed of a high gloss presenting a novel, graphic effect.

The coating composition is desirably employed in high solids aqueoussuspensiomsuch as from about 40% t'o about and preferably from about 55%to about 65% solids, and can be employed in such high concentration dueto its milk-like fluidity due to the presence of rubber latex. On a dryweight solids basis the composition is comprised of from about 5% toabout 20% and preferably from about 10% to about 15% of latex solids,and the balance mineral fillers such as clay and opacifying pigment suchas titanium dioxide, satin white, lithopone, and the like. Small amountsof adjuvants may be added such as minor amounts of clay dispersingagent, latex stabilizing agents, a'ntifoaming agents, and the like. Thelatex may be of natural rubber or of a synthetic rubbe'r, such asthebutadiene-styrerie orbutadiene-acrylonitrile copolyniers,polyclilo'rop'rene, polyisobutylene,

surface, followed by waxing both faces. The

present invention, this machine butyl rubber, and the like. These areemployed in commercial aqueous dispersions or suspensions and necessarywater is added to the latex-opacifying mineral mix to provide desirablesolids content.

The following is a typical example of a suitable coating composition:

' The foregoing composition has a solids content of about 55.5%. Thesodium tetraphosphate (Quadrafos) is used as a dispersing anddeflocculating agent for the minerals. The casein is used as a latexstabilizing or anticoagulating agent, and other protein materials may beused for this purpose. The ammonia is used to preserve alkalinity of thecomposition and as an adjuvant for the casein. If desired, antifoamingagents may be added, such as about 50 cc. of an aqueous solution oftributylphosphate or an alkaline aqueous emulsion of a drying oil. Theaddition'of two parts by weight of an emulsion composed of one partlinseed oil, one part water and a minor amount of ammonium hydroxide hasbeen found particularly useful as an antifoaming agent. The latex notonly acts as the principal hinder or adhesive for the coatingcomposition, but provides the end sheet with a desirable softness orpliability. Further, due to its oil resistant nature, it minimizes theamount of printing ink subsequently required, which is a matter ofcons'iderable economy.

Referring to the drawing, the reference numeral 10 indicates a newlyformed wet web after leaving the Fourdrinier wire, either in the normalcondition of about 70% moisture content, or in a partially dried but notlessv than about 50% moisture content condition if predryers, not shown,are employed. The wet web is then transferred by means of the roll 11 tothe large polished surface, steam-heated Yankee drum dryer 12 andcarried thereon aboutthe major portion of its peripheral surface untilit'is stripped therefrom over the roll 13. Stripping is accomplished bymeans of the driven rolls of the calender stack 14. This calender stackmay be replaced by a single pair of driven pinch rolls, not shown, fordrawing the paper from the drying drum 12. In the alternative thelowermost two rolls of the illustrated stack may be employed for thispurpose. As illustrated, the paper passes through several nips which mayoptionally be desirable for the purpose of densifying the web so as toreduce its absorbency to wax with which the sheet is to be ultimatelysaturated.

The web after it leaves the Yankee drum 12 is preferably in a fullydried condition, i. e., having a moisture content of about The surfaceof the web which was maintained in contact with the polished face of thedrying drum 12 is now machine glazed and is of a porous nature due tothe unidirectional vaporization of moisture content from the web whilewrapped about the drum. The web is further of a translucent character,being either unfilled or but partially filled with opacifying mineralpigment, i. e., about one-third of that normally required foropacification. If desired, although not essential, some opacifyingcoating composition material of conventional character may be applied tothe outer face of the web as it passes around the drum 12 by means ofthe diagrammatically indicated roll coating means 15.

Thereafter a latex-containing opacifying coating composition is appliedto the glazed surface of the web. Al-

though the dried web 10 may be reeled up after being drawn from thedrying drum and subsequently subjected to coating on its machine-glazedside, it will be apparent that such operation is economicallyunadvantageous, and it is therefore preferred that the entirepaper-making, drying and coating operation be carried out in acontinuous process flow, as diagrammatically illustrated. When, forexample, employment is made of a drying drum of about twelve feet indiameter and the web is applied thereto in a condition of maximummoisture content as it leaves the Fourdrinier dryer, the completeoperation may be carried out at speeds of about 500 feet per minute.Speeds in excess of 500 to about 1000 feet per minute may beaccomplished in a continuous operation if the Wet web as it leaves theFourdrinier dryer is subjected to partial predrying, as previouslyindicated.

The dry web after it leaves the lowermost two rolls of the calenderstack 14, or an equivalent pair of pinch rolls, is drawn with itsmachine glazed surface downward over the coating applicator roll 16,which may be a hard surface roll revolving in the fountain 17 holding asupply of latex-mineral pigment opacifying composition 18 of thecharacter previously described. This applicator roll 16 is preferablydriven by means of a variable speed motor, not illustrated, and atapproximately 7% of the paper speed. A vertically adjustable depressingroll 19 brings the paper in contact with the applicator roll. The paperthen passes around the resilient, i. e. rubber covered, backup roll 20and excess coating is removed from the web by means of the fixedlymounted flexible doctor blade 21, whereat excess coating is collected inthe trough 22 and returned to the system, preferably after screening'toremove fibers and other coarse particles, the doctor blade actingagainst the coated web portion in contact with the resilient backup roll20.

The amount of latex-opacifying coating composition is desirablycontrolled so as to apply to the web from about two to about five andpreferably about three pounds of coating composition per three thousandsquare feet (i. e., a ream of 500 24 x 36 inch sheets). Amounts lessthan two pounds do not provide adequate coverage and opacifying, andgreater than five pounds have a tendency to cause streaking and mottlingor graininess. Depending upon the speed of the web, and the weight ofcoating desired to be applied, the spacing between the point of coatingapplication and removal of excess may be varied,

so as to permit a variation in the interval for absorption by the porousWebof a requisite amount of coating composition. This may beaccomplished by moving the applicator in a horizontal position, asillustrated by the dotted lines, or, in the alternative, by shifting theposition of the doctor blade, as for example further illustrated by thedotted lines indicating alternate position of the doctor blade. Means,not shown, are provided for adjusting the angle and pressure of thedoctor blade with respect to the backup roll, and to further permitcleaning of the blade when necessary.

After the web has absorbed the requisite amount of coating compositionand the excess has been doctored off, the coated web is subjected todrying. In order to prevent sticking of the moist, coated surface of theweb, to means such as steam-heated drying drums, the web'is first passedbetween spaced dryers 23-23 which may comprise banks of infrared lampsor air jets. The coated web may be fully dried in this manner, orpreferably drying may be accomplished in this manner to an extent onlyadequate to insure prevention of sticking of the coated surface to asubsequently employed drying drum.

Thus, as illustrated, after the web passes between the banks of dryers23, it passes over the roll 24 and the coated surface of the web comesin contact with the face of the steam drying drum 25, whereat it iscompletely dried and then wound up on the reel 26. The drying drum 25may, for example, be one of about four feet in diameter, and it will benoted that the coated surface of the web is brought into contact withthe face of the drying drum so as to insure retention of a smoothsurface. As a further alternative, the banks of infrared lamps or airjet dryers 23 may be dispensed with and the roll 24 may be replaced by asteam drying drum which, as illustrated, will first contact the uncoatedface of the web and thus dry it to an extent that the coated surface ofthe web can then be safely brought into contact with the face of thedrum 25.

As a further alternative, when the wet web is subjected to partialpredrying, as previously indicated, and greater speeds are employed, aplurality of final drying drums may be employed. During the dryingoperation, particularly in the final step thereof where the coating isbrought into contact with the surface of the steam-heated drying drum25, the rubber latex under the influence of the heat becomessuificiently dry to provide proper adhesive strength for the coatingcomposition.

The finally dried paper is of an extremely smooth and highly glazedsurface which requires no further calendering or supercalendering andmay be subjected to final printing and wax impregnation without furthertreatment. The coated, machine glazed surface is now of an exceptionallysmooth character. Due to the nature of its rubber-mineral pigmentcomposition it is receptive to extremely fine line printing by means ofminimum amounts of printing inks. After printing the sheet may besaturated or impregnated with conventional wax, such as parafiin waxgenerally employed in the manufacture of opaque waxed Wrapping papers,such final printed and waxed product taking on a final solid appearanceand a bright, novel, graphic effect.

I claim as my invention:

1. The method of making opaque coated paper of enhanced physicalproperties and printability adapted for the production of waxed foodwrapping which comprises coating a sheet of thin, porous, absorbent,translucent paper having a machine glazed surface by applying to saidmachine glazed surface an excess of an aqueous suspension containingmineral filler and opacifying pigment together with rubber latex as theprincipal organic binder therefor, doctoring excess coating from saidsurface after absorption of a portion thereof by the sheet and while thesheet is carried by a resilient moving surface, and then drying theresulting coated sheet.

2. The method of making opaque coated paper of enhanced physicalproperties and printability adapted for the production of waxed foodWrapping which comprises coating a sheet of thin, porous, absorbent,translucent paper having a machine glazed surface by applying to saidmachine glazed surface an excess of an aqueous suspension containingmineral filler and opacifying pig ment together with rubber latex as theprincipal organic binder therefor, doctoring excess coating from saidsurface after absorption of a portion thereof by the sheet and while thesheet is carried by a resilient moving surface, drying the resultingcoated sheet, imprinting the resulting coated surface, and then waxingthe printed sheet.

3. The method of making opaque coated paper of enhanced physicalproperties and printability adapted for the production of printed waxedfood wrapping, which comprises applying an excess of an aqueoussuspension of mineral filler and opacifying pigment containing rubberlatex as the principal organic adhesive therefor, to the machine glazedsurface of a continuously moving web of thin, porous, absorbent,translucent machine glazed paper, moving the web forwardly to bring itsopposed face into contact with a moving resilient supporting surface andthereat wiping excess coating composition from the coated face of theweb, and then drying the coated web.

4. The method of making opaque coated paper of enhanced physicalproperties and printability adapted for the production of printed waxedfood wrapping, which comprises applying an excess of an aqueoussuspension of mineral filler and opacifying pigment containing rubberlatex as the principal organic adhesive therefor, to the machine glazedsurface of a continuously moving web of thin, porous, absorbent,translucent machine glazed paper, moving the web forwardly to bring itsopposed face into contact with a moving resilient supporting surface andthereat wiping excess coating composition from the coated face of theweb, and then drying the coated web by first subjecting it to partialheat drying with the web coating spaced from a heated surface and thento complete drying with the coating in direct contact with a movingheated surface.

5. The method of making opaque coated paper of enhanced physicalproperties and printability in a continuous paper-making process, whichcomprises continuously applying an excess of an aqueous suspension ofmineral filler and opacifying pigment containing rubber latex as theprincipal organic adhesive therefor, to the machine glazed surface of aforwardly moving newly formed dry web of thin, porous, absorbent,translucent, machine glazed paper, bringing the opposed face of the webinto contact with a moving resilient supporting surface spaced from thepoint of coating application, and thereat resiliently doctoring offexcess coating composition, while correlating the solids content of thecoating composition, speed of web travel and spacing between the pointof coating application and doctoring to control the amount of coatingabsorbed by the web, and then heat drying the coated web by firstpartially removing its moisture while maintaining its coated face spacedfrom a heated surface, and then to complete drying by applying thecoated face to a moving heated surface.

References Cited in the file of this patent UNITED STATES PATENTS1,982,018 Owen Nov. 27, 1934 2,046,975 Shaw et a1. July 7, 19362,132,931 BOhn Oct. 11, 1938 2,244,859 Thiele et a1. June 10, 19412,275,148 Hornbeck Mar. 3, 1942 2,402,605 Cowen June 25, 1946 2,554,899COwgill May 29, 1951

1. THE METHOD OF MAKING OPAQUE COATED PAPER OF ENHANCED PHYSICALPROPERTIES AND PRINTABILITY ADAPTED FOR THE PRODUCTION OF WAXED FOODWRAPPING WHICH COMPRISES COATING A SHEET OF THIN, POROUS, ABSORBENT,TRANSLUCENT PAPER HAVING A MACHINE GLAZED SURFACE BY APPLYING TO SAIDMACHINE GLAZED SURFACE AN EXCESS OF AN AQUEOUS SUSPENSION CONTAININGMINERAL FILLER AND OPACIFYING PIGMENT TOGETHER WITH RUBBER LATEX AS THEPRINCIPAL ORGANIC BINDER THEREFOR, DOCTORING EXCESS COATING FROM SAIDSURFACE AFTER ABSORPTION OF A PORTION THEREOF BY THE SHEET AND WHILE THESHEET IS CARRIED BY A RESILIENT MOVING SURFACE, AND THEN DRYING THERESULTING COATED SHEET.